<html>
<body>
<canvas id="c" width=200 height=200></canvas>
<script>
var c2 = document.getElementById("c");
var ctx_o = c2.getContext('2d');
ctx_o.fillRect(0, 0, 200, 200);
ctx_o.fillStyle="#00FF00";
ctx_o.fillRect(50, 50, 100, 100);

</script>
</body>
</html>
